Several approaches are being taken to develop agents which modulate cellular 0-phosphotyrosine-utilizing signal transduction processes. In one study, which examined the possible inhibition of protein-tyrosine kinases (PTK) by opiates, it was found that (+/-)-phenazocine (1) was a potent inhibitor of epidermal growth factor receptor (EGFR) PTK (IC50 = 12 Micro) with an activity approaching that of erbstatin (IC50 = 5 Micro). (+/-)-Phenazocine represents a potentially important lead in the development of a new class of PTK inhibitors. In a separate study, a series of phosphonate-containing, styrenes (2) was found to be inactive as inhibitors of either EGFR or p56lck PTKs. Additional phosphonate-containing analogues of (4) are being prepared to more fully define the potential of phosphonate-bearing PTK inhibitors. In another investigation, a series of hydroxylated cyano-cinnamamides (5) were prepared and examined for their ability to inhibit various PTKs (p56lck, platelet derived growth factor (PDGF) and insulin receptor). Several analogues exhibited markedly different potencies among the different PTKs, a fact which is being analyzed by computer-generated molecular modeling to determine structural criteria for kinase selectivity and binding to the catalytic site. A series of conformationally constrained analogues (6) is being prepared to further elaborate these results. Finally, a compound, 7, has been prepared as a hydrolytically stable mimetic of 0-phosphotyrosine which is suitably protected for incorporation into peptides using solid-phase techniques. Compound 7 is being used to construct mimetics of 0-phosphotyrosine-containing peptides which are intended as inhibitors of PTK substrate recognition and of 0-phosphotyrosine phosphatases (which are involved in PTK modulation).